shell-automation

Shell Automation Skill

Master shell automation, CI/CD, and deployment scripting

Learning Objectives

After completing this skill, you will be able to:

• Write production-grade automation scripts
• Create effective Makefiles
• Set up CI/CD pipelines
• Build deployment scripts
• Test shell scripts with bats

Prerequisites

• Strong Bash fundamentals
• Git basics
• Understanding of CI/CD concepts

Core Concepts

1. Script Template

#!/usr/bin/env bash
set -euo pipefail
IFS=$'\n\t'

readonly SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
readonly SCRIPT_NAME="$(basename "${BASH_SOURCE[0]}")"

log_info()  { printf '[INFO] %s\n' "$*" >&2; }
log_error() { printf '[ERROR] %s\n' "$*" >&2; }
die()       { log_error "$1"; exit "${2:-1}"; }

usage() {
    cat <<EOF
Usage: $SCRIPT_NAME [options] <argument>
Options:
    -h, --help      Show this help
    -v, --verbose   Enable verbose
EOF
}

main() {
    while [[ $# -gt 0 ]]; do
        case "$1" in
            -h|--help) usage; exit 0 ;;
            *) break ;;
        esac
    done
    log_info "Starting..."
}

main "$@"

2. Makefile Pattern

.PHONY: all build test lint clean help

SHELL := /bin/bash
.DEFAULT_GOAL := help

help: ## Show help
	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | \
		awk 'BEGIN {FS = ":.*?## "}; {printf "%-15s %s\n", $$1, $$2}'

build: ## Build project
	./scripts/build.sh

test: ## Run tests
	bats tests/

lint: ## Run linter
	shellcheck scripts/*.sh

clean: ## Clean artifacts
	rm -rf dist/ build/

3. GitHub Actions

name: CI
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - name: Lint
        run: shellcheck **/*.sh
      - name: Test
        run: bats tests/

4. Bats Testing

#!/usr/bin/env bats

setup() {
    source "./functions.sh"
    TEST_DIR="$(mktemp -d)"
}

teardown() {
    rm -rf "$TEST_DIR"
}

@test "function returns success" {
    run my_function "arg"
    [ "$status" -eq 0 ]
}

@test "output contains expected" {
    run my_function "arg"
    [[ "$output" == *"expected"* ]]
}

Common Patterns

Deployment Script

#!/usr/bin/env bash
set -euo pipefail

deploy() {
    local version="${1:-$(git describe --tags)}"

    log_info "Deploying $version"

    # Pre-flight checks
    preflight_check

    # Create backup
    create_backup

    # Deploy
    rsync -avz --delete dist/ /opt/app/

    # Restart service
    systemctl restart app

    log_info "Deployed $version"
}

rollback() {
    local previous
    previous=$(ls -t /opt/backups | head -1)
    log_info "Rolling back to $previous"
    rsync -avz "/opt/backups/$previous/" /opt/app/
    systemctl restart app
}

Retry Pattern

retry() {
    local max="${1:-3}"
    local delay="${2:-1}"
    shift 2

    for ((i=1; i<=max; i++)); do
        if "$@"; then
            return 0
        fi
        log_info "Retry $i/$max in ${delay}s..."
        sleep "$delay"
        delay=$((delay * 2))
    done
    return 1
}

# Usage
retry 5 2 curl -sf https://api.example.com

Anti-Patterns

Don't	Do	Why
Skip ShellCheck	Always lint	Catch bugs
No error handling	Use set -e	Fail early
Hardcode paths	Use variables	Flexibility
Skip tests	Write bats tests	Reliability

Practice Exercises

1. Deploy Script: Zero-downtime deployment
2. Backup System: Automated backups with rotation
3. CI Pipeline: Complete GitHub Actions workflow
4. Test Suite: Comprehensive bats tests

Troubleshooting

Common Errors

Error	Cause	Fix
Script not running	Not executable	chmod +x
Command not found	PATH issue	Use full path
Syntax error	Missing quotes	ShellCheck

Debug Techniques

# Enable trace
set -x

# Run with debug
bash -x script.sh

# ShellCheck
shellcheck script.sh

Resources

• Bash Strict Mode
• ShellCheck
• Bats Testing
• GitHub Actions